Senecio jacobaea is an herbaceous biennial that can grow 20 cm-1 m (8 in.-3.3 ft.) in height. The plant starts out as slightly tomentose, but becomes glabrous by the time it is in full flower. The leaves of the basal rosette look similar to the lower stem leaves, but with reduced internodes. The alternately arranged leaves of the plant are pinnatifid in shape, with the lower leaves having
petioles and the upper leaves being sessile. The leaf lobes are oblong and web-shaped. The margins of the leaves are dentate. The leaves can measure between 4-20 cm (1.5-8 in.) long and 2-6 cm (0.75-2.25 in.) wide. The upper surface of the leaves is a medium green color, while the lower surface is lighter in color and sometimes tomentose.
There are numerous yellow flower heads on Senecio jacobaea, which appear in July through October. The flower heads measure 1.25-1.6 cm (0.5-0.67 in.) across. They are peduncled and arranged in short, compact corymbs. Each flower head has about 12-15 rays. The rays measure 4-8 mm (0.15-0.3 in.). The involucre measures 4 mm (0.15 in.) in height. The bracts are linear-lanceolate in shape and green, often with a black tip. The fruits are are light brown achenes that measure 2 mm (0.08 in.) long. There are two types of achenes present in Senecio jacobaea. Those produced by disk florets are located at the center of the flower, and have a white pappus that measures from 4 to 5 mm (0.15-0.2 in.) long. Those produced by ray florets at the margin of the flower head do not have a pappus.
Page References Fernald 1532, Gleason & Cronquist 559, Holmgren 526,
Magee & Ahles 1031, Newcomb 378, Peterson & McKenny 176. See reference section below for full citations.

Senecio jacobaea is native to most of Europe, North Africa and western Asia. It has been introduced into New Zealand, Australia, South Africa, North and South America. In Canada, it has been reported from Prince Edward Island, Nova Scotia, and New Brunswick. In the United States, it has been found in the west in California, Oregon, Washington, Idaho, Montana, and Wyoming. In the eastern United States it has been found in Michigan, Illinois, Indiana, New York, New Jersey, and Pennsylvania. In New England, it has been reported from Maine and Massachusetts.

HISTORY OF INTRODUCTION IN NEW ENGLAND

The history of introduction of this weed into New England is largely unknown. It was first reported from various ports on the coasts in the 1900s. In 1904, it was reported from a pasture in Portland, Maine. In 1910, there is a record of it from Danvers, Massachusetts in Essex County. It appears that neither the Portland, Maine, nor the Danvers, Massachusetts populations have persisted to the current time. It was reported from Vancouver, Canada in 1913 and Oregon in 1922. It was likely introduced via contaminated hay brought over from Europe. More recently, in 2002, it has been reported from Barre, Massachusetts in Worcester County. However, the plants seem to have been there for some time prior to this recent report. It appears to have come from wool waste that was spread on the farm fields for fertilizer.

Senecio jacobaea relies on disturbance to become established. It is highly tolerant of a variety of soil types, as well as salt, and does not appear to have a preference for any particular type.

THREATS

In the west, Senecio jacobaea is mainly a pest of rangelands, where it can poison cattle and horses. In the 1970s, Oregon lost up to 4 million dollars a year in lost livestock. In the east, it is more of a threat in coastal grasslands as well as pasture land. The plants themselves usually produce 60,000 to 70,000 seeds per plant, with large plants producing 250,000 seeds. These seeds can remain viable for up to 15 years in the seed bank. The plant has not yet become the problem in the east as it has in the west, and steps should be taken to prevent this from occurring.

DOCUMENTATION NEEDS

Documentation required: Herbarium specimen or mounted snippet of a branch with flowers.Best time for documentation: Summer.